1. Technical Field
The invention relates to a welding apparatus for electrical seam welding, with a first electrode roller and a second electrode roller, wherein the welding path of the welding device for the objects to be welded extends between the electrode rollers and wherein a common wire electrode runs on the electrode rollers and adopts a predefined path in the device, wherein the second electrode roller is driven by its own drive for rotating with the adjustable nominal welding speed. Furthermore, the invention relates to a method for electric resistance welding container bodies which pass between a first and a second electrode roller, on which a common wire electrode (25) runs, with at least one of the electrode rollers being driven, as well as a preferred use of the method for seam welding of container bodies.
2. Prior Art
Seam welding devices are known and are for example used for manufacturing can bodies, this also being a preferred field of use of the present invention. In case of welding can bodies, the can bodies are transported between the welding electrode rollers with high speed and with as small as possible distances between subsequent bodies. The can bodies, which at the beginning are open along their later longitudinal welding seam, are forced to close on their way towards the welding zone by a so-called Z-rail and in the welding zone by welding tools and are brought into the welding zone with a defined overlapping of the longitudinal edges of the body, in which zone the electric resistance welding with the electrode rollers takes place. A common wire electrode runs on the electrode rollers, which is freshly supplied from a supply roll and is disposed of after the welding as used material. The lower electrode roller arranged at a welding arm is located inside the can bodies to be welded and is not actively driven by an own drive but indirectly via the wire electrode and the can bodies. The upper electrode roller, which is located outside the body to be welded, is driven by an active drive with the desired nominal welding speed. Such devices are known and are described for example in DE 40 31 825 A1. In this document, a path of the wire electrode in a welding device according to the prior art is also shown. Is has to be noted that the welding quality, particularly in the presence of a high throughput speed of hundreds of can bodies per minute, is strongly influenced by possible speed differences between the lower and the upper electrode rollers, even when this difference is small.